The present invention relates to a signal converting device and a method thereof, and more particularly to a signal converting device with harmonic rejection and a related harmonic rejection method.
In a wireless communication system, an oscillating signal having an oscillating frequency can be utilized to mix with a radio frequency (RF) signal to convert the RF signal into a converted RF signal. For example, in a receiver, a received RF signal is down-converted into a baseband signal by mixing the receiving RF signal with an oscillating signal having an oscillating frequency of the carrier frequency of the received RF signal. However, when the oscillating signal is not an ideal oscillating signal with the oscillating frequency, e.g., when the signal with harmonic frequency exists in the oscillating signal, the signal with harmonic frequency may mix with the interference signal to generate another down-converted signal near to or overlapping the baseband signal. Then, the wanted baseband signal may be contaminated by the down-converted interference signal. In other words, the signal with harmonic frequency may degrade the noise figure of the baseband signal. Therefore, how to reduce the effect caused by the harmonic signal of the oscillating signal in the wireless communication system has become an important issue in this field.